The present invention relates to saber saws. Various saber saws have been conventionally developed to cut or saw woody or steel materials or pipes in the housing or building construction sites or similar fields.
Conventional saber saws are basically classified into first and second types. According to a saber saw of the first type, a saw blade is reciprocated along a linear path. According to a saber saw of the second type, a saw blade is moved along an orbital path, for example, an elliptic path. The second type is also referred to as the orbital cutting type.
The conventional saber saws of the orbital cutting type, for example disclosed in U.S. Pat. No. 3,945,120 and in U.S. Pat. No. 3,461,732, are preferable to cut relatively soft material, such as woody members.
FIG. 1 shows a conventional saber saw of the orbital cutting type. A secondary shaft 109 is driven by a drive shaft 108 (of a motor or a comparable driving source). The secondary shaft 109 is provided with an eccentric shaft portion 109b. A wobble plate 118 is attached around the secondary shaft 109. The wobble plate 118 converts the rotational motion of the secondary shaft 109 into a reciprocative movement. A saw blade 127 is attached to the front end of a plunger 120. The plunger 120 is slidably coupled in a guide sleeve 113. The guide sleeve 113 is swingable about its pivot xe2x80x98Axe2x80x99 defined by an axis which is perpendicular to the guide sleeve 113 and is fixed to a gear cover 106. When the secondary shaft 109 rotates, the plunger 120 reciprocates in the back-and-forth direction in accordance with the motion converting mechanism of the wobble plate 118 which converts the rotation of secondary shaft 109 into the reciprocation of plunger 120.
A link plate 135 is attached to a rear portion of guide sleeve 113. The link plate 135, extending downward from the guide sleeve 113, has a distal end. The distal end of link plate 135 is brought into contact with the eccentric shaft portion 109b of secondary shaft 109. During sawing operation, the saw blade 127 receives a reaction force F1 which causes a clockwise moment about the pivot xe2x80x98Axe2x80x99 of guide sleeve 113. The rear end of guide sleeve 113 moves downward. The distal end (i.e., lower end) of link plate 135 is depressed against the eccentric shaft portion 109b of secondary shaft 109. The eccentric shaft portion 109b rotates in accordance with the rotation of secondary shaft 109. The rotation of eccentric shaft portion 109b is transmitted to the guide sleeve 113 via the link plate 135. Thus, the guide sleeve 113 swings in the up-and-down direction. As a result, the plunger 120 causes a mixed motion of the reciprocative motion and the swing motion.
The moving path of the saw blade 127 realized by the above-described mixed (i.e., reciprocative/swing) motion of the plunger 120 is dependent on the setting of a phase angle of eccentric shaft portion 109b relative to the plunger 120. FIG. 2 shows an orbital path of the saw blade 127 realized by the above-described mixed (i.e., reciprocative/swing) motion of the plunger 120.
According to the orbital sawing operation shown in FIG. 2, the saw blade 127 chiefly cuts into a material 136 when the saw blade 127 is drawn toward the saber saw body (i.e., during the cutting stroke). This improves the efficiency of cutting work for sawing a wood or a relatively soft material.
FIG. 3 shows an ordinary sawing operation of a saber saw. A saw blade 127 with sawteeth is attached facedown to the front end of a saber saw body held by a user (not shown) in an upright position. FIG. 4 shows another sawing operation of a saber saw held by a user (not shown) in an upside-down condition. The saw blade 127 is inversely attached to the saber saw body.
According to the above-described conventional saber saw of the orbital cutting type shown in FIG. 1, the sawing operation cannot be performed properly if the saw blade 127 is inversely attached to the saber saw body. More specifically, as shown in FIG. 5, the saw blade 127 receives a reaction force F2 from the material 136 under the condition where the saber saw is held in the upside-down condition. The reaction force F2 causes a clockwise moment about the pivot xe2x80x98Axe2x80x99 of guide sleeve 113. The rear end of guide sleeve 113 moves downward. The distal end (i.e., an upper end in this case) of link plate 135 is released from the eccentric shaft portion 109b of secondary shaft 109. Thus, the rotational motion of eccentric shaft portion 109b is not transmitted to the guide sleeve 113. The plunger 120 does not cause a swing motion. The saw blade 127 attached to the front end of plunger 120 cannot move along an orbital path.
The saber saw disclosed in U.S. Pat. No. 3,945,120 discloses a member equivalent to the link plate 135 rotatably attached to the eccentric shaft portion 109b. If the linking mechanism disclosed in U.S. Pat. No. 3,945,120 is employed in the saber saw shown in FIG. 1, the plunger 120 will swing in the up-and-down direction even when the saw blade 127 is inversely attached to the saber saw body. The saw blade 127 will move along an orbital path shown in FIG. 6. However, in this case, as better understood from the comparison between FIG. 2 and FIG. 6, the saw blade 127 moves in the opposite direction (refer to the direction of arrow) due to the unchanged phase relationship between the eccentric shaft portion 109b and the plunger 120.
According to the orbital sawing operation shown in FIG. 6, the saw blade 127 cannot smoothly cut into the material 136 when the saw blade 127 is drawn toward the saber saw body (i.e., during the cutting stroke) because the saw blade 127 moves along an upper arc line far from the material 136.
In this manner, none of the conventional saber saws teach a technical solution for enabling proper orbital sawing operation even when the saw blade 127 is attached inversely to the saber saw body.
The applicant""s copending application Ser. No. 09/468,127, now patented as U.S. Pat. No. 6,282,797, discloses a saber saw of the orbital cutting type which can operate properly even when a saw blade is inversely attached to a plunger or a carrier.
PCT internal publication No. WO 98/07544 discloses a saber saw that approaches the better cutting performance of orbital saws without the complexity required for orbital motion and achieves a forward motion of the saw blade during the cutting stroke without resorting to orbital motion.
The proposed saber saws are still complicated in structure and need to be more simplified.
In view of the foregoing problems of the prior art, an object of the present invention is to provide a saber saw of the orbital cutting type which can operate properly even when a saw blade is inversely attached to a saber saw body, thereby improving the efficiency of cutting work.
In order to accomplish this and other related objects, the present invention provides a first saber saw comprising a housing for accommodating a motor and a driven shaft rotatably supported by the housing and rotated by the motor. A plunger causes reciprocative motion with respect to the housing. A saw blade is attached to a front end of the plunger. A first motion converting mechanism, interposed between the driven shaft and the plunger, converts the rotational motion of the driven shaft into the reciprocative motion of the plunger. A second motion converting mechanism, interposed between the driven shaft and the plunger, converts the rotational motion of the driven shaft into the swing motion of the plunger. A plurality of eccentric shaft portions are formed on the driven shaft. The second motion converting mechanism includes contact portions selectively brought into contact with the eccentric shaft portions of the driven shaft.
According to a preferred embodiment of the present invention, the first saber saw of the present invention further comprises a guide sleeve. The guide sleeve slidably holds the plunger so as to allow the reciprocative motion and is hingedly supported about a pivot fixed to the housing. The guide sleeve can swing in a direction normal to a reciprocating direction of the plunger. The second motion converting mechanism includes a guide member attached to the guide sleeve. The guide member has the contact portions selectively brought into contact with the eccentric shaft portions of the driven shaft.
According to the preferred embodiment of the present invention, the plurality of eccentric shaft portions are two, first and second, eccentric shaft portions formed on the driven shaft. A predetermined phase difference is provided between the first and second eccentric shaft portions of the driven shaft. For example, the phase difference between the first and second eccentric shaft portions is 180xc2x0 or 225xc2x0. The first and second eccentric shaft portions are offset from each other in an axial direction of the driven shaft. An eccentric amount of the first eccentric shaft portion is identical to or different from an eccentric amount of the second eccentric shaft portion.
According to the preferred embodiment of the present invention, the contact portions of the second motion converting mechanism are two, first and second, contact portions selectively brought into contact with first and second eccentric shaft portions formed on the driven shaft. The first and second contact portions are offset from each other in an axial direction of the driven shaft. The first contact portion is opposed to the first eccentric shaft portion and the second contact portion is opposed to the second eccentric shaft portion.
According to the preferred embodiment of the present invention, the second motion converting mechanism includes a locking mechanism for restricting the swing motion of the plunger. The first and second contact portions are released from the first and second eccentric shaft portions when the locking mechanism locks the plunger, thereby keeping the second motion converting mechanism in a neutral condition.
It is also possible that the second motion converting mechanism includes independent or separate guide members for the first and second contact portions.
As a practical example, the guide member of the second motion converting mechanism is a contact plate extending in a cantilever fashion from the guide sleeve toward the driven shaft. The contact plate has a projecting portion and a rectangular ring portion which are formed at a distal end of this contact plate. The driven shaft extends through an opening of the rectangular ring portion of the contact plate. The first contact portion is formed at a distal end surface of the projecting portion. The second contact portion is formed at an inner surface of the rectangular ring portion.
Furthermore, the present invention provides a second saber saw comprising a housing for accommodating a motor and a bevel gear rotatably supported by the housing and rotated by the motor. A plunger causes reciprocative motion with respect to the housing and has a front end to which a saw blade is attached. A guide sleeve slidably holds the plunger so as to allow the reciprocative motion and is hingedly supported about a pivot fixed to the housing. The guide sleeve can swing in a direction normal to a reciprocating direction of the plunger. A first motion converting mechanism, interposed between the bevel gear and the plunger, converts the rotational motion of the bevel gear into the reciprocative motion of the plunger. A second motion converting mechanism, interposed between the bevel gear and the plunger, converts the rotational motion of the bevel gear into the swing motion of the plunger. First and second slant surfaces are formed on the bevel gear. The second motion converting mechanism includes a guide member attached to the guide sleeve. The guide member has first and second contact portions selectively brought into contact with the first and second slant surfaces of the bevel gear.
It is preferable for the second saber saw that the guide member of the second motion converting mechanism is a contact plate extending in a cantilever fashion from the guide sleeve toward the bevel gear. The contact plate has the first contact portion opposed to the first slant surface of the bevel gear and the second contact portion opposed to the second slant surface of the bevel gear.